In the construction of naturally lit structures (e.g., greenhouses, pool enclosures, solar roof collectors, conservatories, stadiums, sunrooms, and so forth), glass has been employed in many applications as transparent structural elements, such as, windows, facings, and roofs. Glass panels of glass panel roofs can themselves be mounted in frame-like enclosures that are capable of providing a watertight seal around the glass panel and provide a means for securing the panel to a structure. These frame-like enclosures also provide for modular glass roofing systems that can be assembled together to form the roof. However, polymer sheeting is replacing glass in many applications due to several notable benefits.
Glass panel roofing systems generally provide good light transmission and versatility. However, the initial and subsequent costs associated with these systems limit their application and overall market acceptance. The initial expenses associated with glass panel roofing systems comprise the cost of the glass panels themselves as well as the cost of the structure, or structural reinforcements, that are employed to support the high weight of the glass. After these initial expenses, operating costs associated with the inherently poor insulating ability of the glass panels can result in higher heating expenses for the owner. Yet further, glass panels are susceptible to damage caused by impact or shifts in the support structure (e.g., settling), which can result in high maintenance costs. This is especially concerning for horticultural applications wherein profit margins for greenhouses can be substantially impacted due to these expenditures.
Multiwall polymeric panels have been produced that exhibit improved impact resistance, ductility, insulative properties, and comprise less weight than comparatively sized glass panels. As a result, these characteristics reduce operational and maintenance expenses. One benefit of polymer sheeting is that it exhibits excellent impact resistance compared to glass. This in turn reduces breakage and hence, maintenance costs in applications wherein occasional breakage caused by vandalism, hail, contraction/expansion, and so forth, is encountered. Another benefit of polymer sheeting is a significant reduction in weight compared to glass. This makes polymer sheeting easier to install than glass and reduces the load-bearing requirements of the structure on which they are installed. In addition to these benefits, one of the most significant advantages of polymer sheeting is that it provides improved insulative properties compared to glass. This characteristic significantly affects the overall market acceptance of polymer sheeting as consumers desire structural elements with improved efficiency to reduce heating and/or cooling costs.
Multiwall sheets can display high stress around the edges of the multiwall sheet for a given wind load as well as high deflection. Multiwall sheets can also have undesirably low flexural stiffness. Multiwall sheets that possess adequate flexural stiffness, lower stress around the edges, and decreased deflection with a nominal or no increase in weight are desired in the industry.